In industrial sites where waste oil and sewage are generated in large quantities and constantly, waste oil and sewage are separated from each other and then processed individually in various ways such as a specific gravity separation method, a hydraulic separation method, etc. depending on the amount of waste oil and sewage to be processed, the frequency of processing, and the type.
However, sewage generated in single-family houses, multi-family houses, roads, parking lots, gas stations, restaurants, etc. (oil and wastewater generated during cooking of various kinds of oil) is irregular in volume or too small to process using an industrial method. Thus, the oil and sewage flow into a manhole without being separated and discharged to the wastewater treatment plant together through the sewage pipe.
Due to its high viscosity, oil solidifies as a lump together with other materials to deposit an inner wall of the sewage pipe or the manhole. Thereby, a diameter of the pipe is gradually narrowed and clogged, causing a drainage issue. This results in complaints from residents and municipalities, and it costs a great deal of money to handle the issue.
When the solidified oil lumps are introduced into the wastewater treatment plant along with the wastewater, its high viscosity put a high load on the pump which transports the wastewater in the wastewater treatment plant. Thus, purification efficiency deteriorates when an oil sewage is mixed with a water sewage are processed together.
To solve this problem, an oil separation chamber is installed in the manhole to separate the oil sewage from the water sewage. The oil sewage is collected in an oil storage tank located at a bottom of the manhole and discharged, to the outside. The water sewage is discharged from the manhole to a sewer line. Alternatively, when the oil-water mixture sewage is introduced into the manhole, the oil-water mixture sewage is separated into the oil sewage and the water sewage by a specific gravity difference. The oil sewage has a lower specific gravity than the water and thus floats on the water sewage. The water sewage is then discharged to a discharge pipe, and the oil sewage is collected separately and removed using a central cleaning system.
However, the water-oil separation using a specific gravity difference is not effective when the mixture sewage temperature is hot. In a conventional structure or system, an external air is not provided into the hot sewage. Thus, the oil-water mixture sewage remains hot in the manhole. As a result, the separation efficiency is poor. For this reason, a natural separation method is not popular. Even if it is employed, its performance was bad.